Study On The Preparation Of Spent Bleaching Earth Carbon-based Materials And The Removal Of Organic Pollutants From Aqueous Solution

Spent bleaching earth（SBE）is a solid waste produced by the vegetable oil refining industry,containing 20-40 wt%residual oil,and it should be handled properly,otherwise it will cause environmental pollution and waste of resources.The resource utilization of SBE as a starting point,this study prepared three kinds of SBE-based materials including spent bleaching earth carbon（SBE/C）,acid modified spent bleaching earth carbon（HSBE/C）and iron modified spent bleaching earth carbon（Fe-SBE/C）,and to study their removal characteristics of two typical organic pollutants（Eosin Y and Bisphenol A）in water,respectively.Meanwhile,based on the characterization of the materials’morphology,composition,surface functional group,surface charge and so on,the mechanism of adsorption was deduced.The contents of this research mainly include::（1）Using spent bleaching earth（SBE）as a raw material,and renewable spent bleaching earth carbon（SBE/C）was prepared by high temperature pyrolysis method,which was used for the adsorption removal of organic pollutant Eosin Y from water.The adsorption kinetics and the adsorption isotherms of the adsorption of Eosin Y by SBE and SBE/C were in accordance with the Pseudo-second-order kinetic model,the Langmuir isotherms model and the intraparticle diffusion model,the Freundlich isotherms model,respectively.The maximum adsorption capacity of SBE/C（11.15 mg/g）was much higher than SBE（4.04 mg/g）.The adsorption capacity of SBE/C decreased with increasing temperature,and the physical adsorption was dominant.The adsorption capacity of SBE/C for Eosin Y was limited by the pH of the solution,while the pH had a great influence on the adsorption capacity of SBE for Eosin Y（the adsorption capacity decreased with the increase of pH,when the initial pH of the solution increased from 5 to 12,the adsorption capacity of SBE for Eosin Y decreased from 5.32 mg/g to 0.22 mg/g）.The coexisting cations had a negative effect on the adsorption of SBE and SBE/C,and the order of the influence of each ion was as follows:Mg²⁺<K⁺<Na⁺;the coexisting anions had the same degree of adsorption inhibition on SBE/C,and the inhibition trend of each ion was as follows:PO₄^3->CO₃^2->NO₃^->SO₄^2->Cl^-.The high temperature pyrolysis maked the oil carbonized and increased the specific surface area of SBE/C（102.19 m²/g）.Electrostatic interaction,hydrogen bond,halogen bond andπ-πinteraction will be formed between SBE,SBE/C and Eosin Y.The adsorption of Eosin Y on SBE/C was dominated by these interactions and hydrophobic interactions,while SBE was most affected by electrostatic interactions.The NaOH desorption method was used to regenerate SBE/C.After three adsorption-desorption cycles,the adsorption capacity of SBE/C was maintained at 56%,and SBE/C will completely lose adsorption capacity after about 7 cycles.In addition,SBE/C avoided the secondary pollution problem caused by SBE releasing organic matter in water.（2）Using spent bleaching earth carbon（SBE/C）as a raw material,the modified spent bleaching earth carbon was prepared by hydrofluoric acid treatment method（HSBE/C）,which was used for the adsorption removal of bisphenol A（BPA）from water.Hydrofluoric acid treatment eroded the material surface and significantly increased the specific surface area of the material（183.56 m²/g）.The adsorption of BPA on HSBE/C conforms to the Freundlich isotherm model and Pseudo-second-order kinetic model,and its maximum adsorption capacity was 103.92 mg/g was better than that of the commercially available activated carbon（20.00 mg/g）,reaching adsorption equilibrium at about 50 min.The adsorption was a little affected by the temperature and pH,but it was suppressed at the high pH value（>10）.Five kinds of coexisting cations(Na⁺,K⁺,Mg²⁺,Ga²⁺,Al³⁺)and three kinds of coexisting anions(Cl^-,NO₃^-,SO₄^2-)had little effect on adsorption;however,the other coexisting anions(CO₃^2-and PO₄^3-)had obvious inhibition effect on adsorption.When CO₃^2-and PO₄^3-（0.01 mol/L）were present in the solution,the adsorption capacity decreased by 33.15 mg/g and 55.94 mg/g,respectively.The inhibitory effect increased with the increase of ionic strength.The main adsorption mechanism was hydrogen bonding and electrostatic interaction,the influence ofπ-πinteraction was weak.The NaOH desorption regeneration method was better than the re-pyrolysis regeneration method.The adsorption capacity of materials regenerated by NaOH method was only 5.73%lower than that of fresh HSBE/C after three adsorption-desorption cycles,and it will have 54 times for reuse potential.HSBE/C as an environmentally friendly material did not cause secondary pollution to water.（3）Using spent bleaching earth carbon（SBE/C）as a raw material,the iron modified spent bleaching earth carbon（Fe-SBE/C）was prepared by loading zero-valent iron（Fe⁰）onto the material surface by liquid phase reduction method,and a heterogeneous Fenton reaction system with Fe-SBE/C as the core was constructed for catalytic oxidation to remove endocrine disruptor BPA water.Under the reaction conditions(m_c:m_Fe=3:1,pH=3.5,the concentration of hydroxylamine hydrochloride（HAHC）and hydrogen peroxide（H₂O₂）in the solution were 0.05 mmol/L and 0.8 mmol/L,respectively),Fe-SBE/C had better catalytic performance than zero-valent iron（Fe⁰）and has higher removal capacity than the homogeneous Fenton system.The removal efficiency of BPA for Fe-SBE/C+HAHC+H₂O₂ reaction system（C₀=20 mg/L）was about 95%,and the removal efficiency of NPOC was about 70%.When HAHC was present in the system,the removal efficiency of BPA and NPOC were increased,which may be because HAHC enhanced the circulation between Fe（III）/Fe（II）in the system.Through free radical scavenging experiments,it was confirmed that·OH was the main active substance during the degradation process,which led to the degradation of BPA.